When Big Ben struck midnight, its bells didn't just signal the start of a new day. They also marked a sea change in geopolitics.

That was the moment Prime Minister Theresa May chose to sign a letter of intent that officially begins the UK's departure from the EU. The date had been marked on everyone's calendars since the UK voted to break away from the EU on June 30 of last year. Thus, with a stroke of her pen, May made March 29 an historic day.

The world was ready. Papers around the world prepped their best Brexit front pages, with everything from a serious-looking royal guardsman to the Queen herself, wading alone on a small raft in the English Channel, waving goodbye the continent. One government official in Brussels told Politico Europe that other EU countries just want Britain "out now, no matter how much pain it will cause — a bit like the ninth month of pregnancy."

Only the beginning

Expect the Kingdom's government-sanctioned middle finger to dominate headlines all day and the rest of the week. The Independent wrote a mock version of May's letter, in which she writes to European Council President Donald Tusk that she simply wants two things: "1. All of the good stuff. 2. None of the bad stuff." The EU will respond to Britain by the end of the week.

Britain's uncharted journey out of the EU (the Lisbon Treaty article that details the EU-exit process is only five paragraphs) will be a lengthy, often boring and contentious saga that will last two years — possibly more. A Le Monde editorial said the negotiations will perhaps be "the most complicated of all time."

The Financial Times has a projected timeline of the process, and the BBC answered all the basic Brexit questions you might be too embarrassed to ask. But one thing is sure: March 29 is only the beginning.